Investigation on the Background of a Ge(Li) Detector

An experimental study has been performed to investigate the ultimate limit of the intrinsic background of a Ge(Li) detector. The results obtained in three runs under different experimental conditions are compared and discussed. A tentative interpretation of the various sources of background and of their relative contribution is given. From the measurements performed in an underground laboratory with an attenuation factor for cosmic rays of 106, the ultimate background level appears almost completely due to radioactivity present in the structural materials of the cryostat and shield. An important contribution is attributable to airborne radioactivity due to 222Rn daughters.